[C ++] string :: substr function

Form : s.substr (p, n)

Returns a string, the string s containing n characters copied from the beginning of p (the default value of p is 0, the default value of n is s.size () - p, i.e., without copying the entire default parameters s)

. 1  int main ()
 2  {
 . 3      String A;
 . 4      String s ( " 123456789 " );
 5      
. 6      A s.substr = ( 0 , 5 ); // copy length of the string s starting from bit 0 of 5 string 
. 7      COUT A << << endl; // output 12345 
. 8      
. 9      A = s.substr (); // without copying the entire string is the default parameter S 
10      COUT A << << endl; // output 123456789 
. 11      
12 is      A = s.substr ( . 4 ); // output 56789 
13 is     A << endl << COUT; // single parameter default bit string copied from the beginning to the end of 4 
14 }